Intervalometer calibration checker



Feb. 3, 1948. A. FAHRNER INTERVALOMETER CLIBRATION CHECKER Filed Oct. 16, 1945 Patented Feb. 3, 1948 INTERVALOMETER oALiaArioN anaemia f Joseph A. Fahrner, United States Navy Application October 16, 1945, Serial No. 622,666

1 Claim.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This invention relates'to an electric testing device, and particularlyN to an intervalometer calibration checker.

An intervalometer as used in bombing warfare is a timing device designed for use in an electrical bomb release system to send out electrical impulses to the release units in the system, in order to obtain a desired spacing between bombs on or across the target. The-intervalometer is placed in the electrical bomb release system at a point between the power source and the other operating units in the system, and is operated when the Ybombardiers control switch in the intervalometer circuitis closed. Operating on a condenser charge-discharge theory, the intervalometer alternately connects and disconnects the power source to and from the electrical bomb release system, thus sending out timed impulses. The impulses produced by the operation of the intervalometer are distributed throughout the electric bomb release system by the distributing units of the system. Each impulse operates a release unit in the bomb release system, thus releasing a bomb from the airplane. The number of impulses sent outby the intervalometer and the frequency at which they occur may be varied as desired by the bombardier in the airplane, This intervalometer is regarded as a single wire type, since all impulses are sent out from the intervalometer through a single wire.

The purpose of my device is to check the accuracy of the timed impulses generated by the intervalometer. My device receives said intervalometer impulses and determines their actual frequency. Said actual frequency output can be compared with the required frequency for a corresponding intervalometer setting, and any malfunctioning of the intervalometer corrected.

The figure of the drawing shows a wiring diagram of my invention.

The intervalometer I to be checked is electrically connected to an electrical connector plug 2 which mates with an electrical receptacle connector I5. An impulse from the intervalometer enters the checker through pin B.

Power for supplying both my checker and the intervalometer is provided by transformer 4 coupling a 115 volt (iO-cycle source 5 to lter 5 through a dry disc rectier 'I bridge connected. A single-pole single-throw power switch I3 is provided in the GO-cycle line. The positive output of said lter is connected to terminal 8; the negative output to terminal 9, and grounded at I I3. A battery can be connected across terminals 9 and II, in lieu of the above alternating source,

' if desired. Single-pole double-throw switch I2 provides switching means for cutting in the lter 6 output or the battery source.

Pin C is connected to the positive side of the filter 6 output through switch I2 and variable resistor Iii. A starting push button switch I5 is connected across pins A and C. Resistor I6 is connected to pin B and grounded at Il. Said resistor IE5 is connected across a iilter I8 through a selenium rectier I9 bridge connected, and a capacitor 25.

Across the output terminals of said filter I8 is connected a milliammeter 2t through switch 2I. Said milliammeter 20 is calibrated in feet of spacing between bombs on or across a target, at knots of airplane speed.

The power supply voltage to the intervalometer is iixed by means of variable resistor I4 to a predetermined potential of 28 volts. This voltage is read directly on the meter 2l) by a suitable electrical arrangement as follows. A resistor 22 is connected between the remaining terminal 23 of single-pole double-throw switch 2l and variable resistor I4. This multiplier resistor 22 in series with the milliammeter changes said meter to a voltmeter. The meter is also calibrated for voltage readings. The potential of 28 volts decided on was obtained by averaging the voltages of various intervalometer installations in different bombers.

In operation, electrical connector receptacle 3 is mated with connector plug 2 thereby connecting the intervalometer to be checked with my intervalometer calibration checker. The power switch I3 and switch I2 are closed to energize the checker and the intervalometer. Switch 2I is depressed on terminal 23 and the voltage adjusted by variable resistor I4 until a voltage reading of 28 appears on meter 20. The spring loaded switch 2I is then released so as to engage with terminal 24, thereby connecting the meter across the output of filter I8 for operation. The start button i5 is pressed, placing the intervalometer in operation. Impulses from the intervalometer enter the checker through pin B, and are fed across grounded resistor I6 and into capacitor 25. The resistor I6 discharges a spark condenser that is an integral part of every intervalometer which if not discharged would give a false reading.

The condenser 25 is discharged into the selenium type rectier I9 where the pulses are rectified. The rectified pulses are then passed into a iilter circuit which smooths out all slow pulses and allows the meter to read a steady value. The amount of charge and discharge of condenser 25 governs the value of current owing through the meter 20.

In actual testing, the intervalometer is set in a position, for example, corresponding to a spacing between bombs of 85 feet across a target; (Due to the designed timing characteristics of the intervalometer, a predetermined number of impulses per second would actuate the bomb release system to achieve said 85 foot spacing.) Said impulses are, however, fed into the checkery for test. If the intervalometer is operatingcorrectly in timing, sufficient current will pass through the meter 20 to indicate 85 feet on the calibrated meter. If the meter needle indicates more or less than 85 on its scale, the intervalometer is out of timing, correspondingly. .a

Next, place the intervalometer in a position corresponding to a spacing between bombs of 42, for example, feet across a target, and repeat the test; iiiterv'aimeter should be operated, several /timsoifeacli position toenable the operatorto obtain an averagjiach position. g f While `I have shown a" particular embodiment of myinveiition, itfwillbe understood, of course, that I 'de "oft wish to"be"lim'ited thereto, since many 'modicatinsmay be'V made, and I, therefore, contemplate'bvthe"appended claim to cover any`"`s`uch niodicatiois'as fall Ywithin the true spirit and scope v`if my. invention.

'lfhe invention described herein may be manufactured and 'iisedvby'orior the Government of the *'UniteclStatI *ofviimeric'a for governmental purposes; without S"all payment, of any royalties What is claimed is:

An apparatus for checking an intervalometer, comprising: a direct current source having a positive and a negative terminal; an electrical connector receptacle having a rst, a second and a third prong; a variable resistor connecting said positive terminal and said rst prong; a switch interposed between said variable resistor and said positive terminal; a, switch connecting -said rst and said second prongs; a discharge ,resistor connecting said third prong and said negative terminal; a filter circuit; a selenium rectier bridge connected across said filter and across said discharge resistor; a capacitor interposed between said rectifier and the positive side of said discharge resistor; a milliammeter connected acrossl the output of said lter; a singlepole double-throw switch interposed between the positive side of said lter and said milliammeter; and a multiplier resistance connecting the remaining terminal of said double-throw switch and the variable resistance.

JOSEPH A. FAHRNER.

REFERENCES CITED The following references are of record in file of this patent:

UNITED STATES PATENTS the Barnette et al Oct. 26, 1943 

